Productivity of apple leaves, depending on the shape of the crown and the pruning times

Abstract

Aims. To determine the influence of pruning terms and methods of crown formation on the productivity of apple trees grown on dwarf rootstock M.9 in intensive plantations of the Right-Bank Forest-Steppe of Ukraine. Methods. Field (data acquisition), statistical using Tukey's test and Pearson's correlation method (data processing and analysis). The experiment was carried out in the garden of the Uman National University of Horticulture for 4 years (2019–2022) with apple trees of ‘Fuji’ and ‘Honey Crisp’ cultivars on dwarf rootstock M.9, planted according to the 4×1 m scheme. The factors studied were crowning shape: slender spindle, ballerina, and French axis; and also the pruning times: winter (0 BBCH) and winter combined with summer (second decade of June, 74 BBCH). Results. The shape of the crown and double pruning significantly affected the specific productivity per unit area of the apple tree leaf surface. A maximum value of 3.1 kg/m² was when forming the crown ballerina with pruning in winter and summer of ‘Fuji’ trees. A 33% higher indicator value was provided in plantations of the ‘Fuji’ compared to the ‘Honey Crisp’, with 30–33% higher crown formation by the French axis and 33% higher by double crown pruning. Specific productivity correlates with the yield and fruit load of trees. The French axis crown formation provided a threefold increase in the leaf index compared to the slender spindle and ballerina formation. Double pruning (winter and summer) increased the leaf index by 17%. The experiment showed a gradual decrease with a minimum in 2022. The main influence on the value of specific leaf area on crown volume was the crown shape (77.5%), where the formation of the ‘French axis’ provided three times higher values compared to other studied crowns. Double pruning (winter and summer) also contributed to an increase in this indicator by 60% compared to pruning only in winter. Conclusions. As a result of the formation of the French axis crown, its dimensions were much more compact, as a result of the peculiarities of its formation, which ensured an increase in the value of the leaf index and the specific leaf surface area per crown volume, but due to its smaller size, the value of specific productivity per leaf surface area was significantly reduced. At the same time, there was a clear tendency to increase these indicators and the introduction of double pruning — in winter and summer.